1. Field of the Invention
The present invention relates to optical coupling systems and more particularly to optical coupling systems configured to couple the maximum amount of light from a monochromator into an optical fiber cable or from a fiber optic cable to a spectrometer.
2. Related Prior Art
Prior art has many methods for focusing incident light onto a specific location. The simplest form is a single lens which takes divergent light that is incident on one surface of the lens and focuses all these light rays at one point, the focal point of the lens. The following United States patents are example of prior art optical focusing systems which are considered relevant to the present invention.
U.S. Pat. No. 4,412,720, titled "Optical System Coupling a Rectangular Light Source to A Circular Light Receiver", issued to Bruno Costa, relates to an optical coupling system wherein a light source of rectangular outline, such as a semiconductor laser, is optically coupled to a light receiver of circular outline, such as an end of an optical fiber. This coupling is done by an anamorphotic system including a pair of spherical lenses and an afocal pair of cylindrical lenses interposed in a telocentric field between the light source and light receiver. When the system is used for measuring the attenuation of a fiber by the back-scattering technique, a semireflecting prism is inserted between the cylindrical lenses and the fiber-side spherical lens to direct part of the returning beam toward a photodetector The effect of spurious reflections at the fiber end may be minimized by the use of a polarizationsensitive Glan prism and/or by the positioning of a flat transparent plate in front of the fiber end.
U.S. Pat. No. 4,475,788, titled "Coupling Between Laser and Optical Fiber", issued to Maurizio Tomassini et al. relates to an optical system used to focus the beam of a laser onto a receiving end of an optical fiber. The laser output is formed by a plano-convex lens with a semi-transparent flat face confronting the laser cavity and an anti-reflecting curved face turned toward the fiber. Alignment of the laser beam with the fiber axis is accomplished by the adjustment of two oppositely pointing juxtaposed wedges placed between the lens and the laser.
U.S. Pat. No. 4,726,645, titled "Optical Coupler", issued to Junichiro Yamashita et al. relates to an optical coupling unit having an optical coupler adapted to couple a light beam from a light-emitting element to an optical fiber. The aberration of the lens is decreased to improve the efficiency of coupling of the light beam from the light-emitting element to the optical fiber. A silicon crystal having a high refractive index is used as a lens material to realize an optical system of low aberration.
U.S. Pat. No. 4,732,450, titled "Input/Output Coupling Device for Optical Fiber Used in High Power Laser Beam Delivery", issued to Chun-Sheu Lee relates to an input/output fiber coupling device for an optical fiber that includes a chamber wall having an opening at one side and a bore at the opposite side. The chamber wall forms a cavity and has a focusing lens that fits within the opening. The lens has input and output laser beam paths aligned with the fiber longitudinal axis, and focuses a laser beam onto the end face of the fiber which is inserted into the cavity through the bore. An indexmatching fluid circulates within the cavity between the lens and the fiber end face.
U.S. Pat. No. 4,744,620, titled "Optical Coupler", issued to Hiroshi Ueno et al. relates to an optical coupler having a lens for coupling a light source and an optical fiber. The lens comprises a transparent column in which a refractive index n(r) at a distance r from an optical axis is expressed by: EQU n.sup.2 (r)=n.sub.0.sup.2 {1-(gr).sup.2 +h.sub.4 (gr).sup.4 +h.sub.4 (gr).sup.6 +h.sub.8 (gr).sup.8 +...}
and satisfies the following conditions when Sf equals g divided by point three; C.sub.1 /Sf is between zero and point sixty-seven; C.sub.2 equals zero; l.sub.1 Sf is greater than or equal to zero and less than or equal to one point five; and h.sub.4 is greater than or equal to point five and less than or equal to two. C.sub.1 and C.sub.2 are curvatures of input and output end faces of the lens (the sign is positive when the center of the radius of curvature is positioned at the side of the optical fiber with respect to the end face). l.sub.1 is a back focus at the side of the light source, n.sub.0 is a refractive index on the optical axis, and g, h.sub.4, h.sub.6 and h.sub.8 are distribution constants.
U.S. Pat. No. 4,753,521, titled "Lens System for Focussing a Divergent Laser Beam", issued to Ulrich Deserno relates to a lens system for focussing a divergent laser beam. This system may be used for converting the three dimensional amplitude and phase distribution of the highly divergent laser beam of a semiconductor laser into the amplitude and phase distribution of the fundamental mode coupleable into a monomode fiber. The lens system comprises a front element in the form of a collecting aplanatic meniscus and one or more following refractive lenses for focussing the laser beam emerging from the front element. The refractive front face of the meniscus facing the object side aberration free point is designed such that it at least approximately has the form of a phase surface of the divergent laser beam emanating from a location close to the object side aberration free point which impinges the meniscus. A tilting of the meniscus relative to the laser radiation causes the part of the divergent laser radiation reflected by the front face to be refocussed next to the source, to provide coupling optics for coupling a semiconductor laser to a fiber.